1999 Honda Accord Knocking Noise

It may of been piston slap. This can happen when the engine is 'cold' because the piston to cylinder wall clearance is at it's maximum when cold, once the vehicle warms the piston expands and the piston stops rattling away.

This also may be valvetrain noise caused by lack of oil pressure on straight up. Have you checked your oil level? What weight oil are you using?

I live in Texas so the cold was definitely not the problem. I had my oil changed last week and I noticed that the oil level dropped slightly.

I took it back to the shop where they changed my oil to have them take a look. After further inspection, they noticed that they did not replace the washer on the drain plug. There was some leakage from this area. They told me that there's no way to check the oil pressure...that makes me wonder. I just now noticed that they put in 10W 30.

Hopefully it did not cause any serious damage. I have since not heard that noise since a couple of days ago.

To check oil pressure you have to remove an oil pressure switch on the back of the engine block and install a mechanical oil pressure gauge. So it's definately not impossible, however it's not a 2 second job either.

Well hopefully everything is fine now. Let us know what happens!